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    <H1 CLASS="title">DualUseFilter</H1>
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<H2>Description</H2>

<P>
    A DualUseFilter is a Filter which can act as an <A HREF="input_filter.html">InputFilter</A> or as an <A HREF="output_filter.html">OutputFilter</A>, but not as both simultaneously. 
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<P>
    DualUseFilters help reduce the number of different Filter types required to implement a particlar filtering algorithm. For example, by implementing <A HREF="../classes/regex_filter.html"><CODE>basic_regex_filter</CODE></A> as a DualUseFilter, the Iostreams library avoids having to define separate templates <CODE>basic_regex_input_filter</CODE> and <CODE>basic_regex_output_filter</CODE>.
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<H2>Refinement of</H2>

<P><A HREF="input_filter.html">InputFilter</A>, <A HREF="output_filter.html">OutputFilter</A>.</P>

<H2>Associated Types</H2>

<TABLE CELLPADDING="5" BORDER="1">
    <TR><TD>Character type</TD><TD>The type of the characters in the filtered sequences</TD></TR>
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        <TD>Category</TD>
        <TD>
            A type convertible to <A HREF="../guide/traits.html#category_tags"><CODE>filter_tag</CODE></A> and to <A HREF="../guide/modes.html#mode_tags"><CODE>dual_use</CODE></A>
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        <TD>Mode</TD>
        <TD>
            The unique <I>most-derived</I> <A HREF="../guide/modes.html#mode_tags">mode tag</A> to which Category is convertible
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<H2>Valid Expressions / Semantics</H2>

Same as <A HREF="bidirectional_filter.html">BidirectionalFilter</A>.

<H2>Exceptions</H2>

Same as <A HREF="bidirectional_filter.html">BidirectionalFilter</A>.

<H2>Models</H2>

<UL>
    <LI>The <A HREF="../guide/text_processing.html">Text Processing Filters</A>.
    <LI>The compression and decompression filters, except for <A HREF="../classes/gzip.html#basic_gzip_decompressor"><CODE>basic_gzip_decompressor</CODE></A>.
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<P CLASS="copyright">&copy; Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>&copy; Copyright 2004-2007 <a href="https://www.boost.org/users/people/jonathan_turkanis.html" target="_top">Jonathan Turkanis</a></P>
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    Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <A HREF="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>)
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